Implantable blood pumps may be used to provide assistance to patients with late stage heart disease. Blood pumps operate by receiving blood from a patient's vascular system and impelling the blood back into the patient's vascular system. By adding momentum and pressure to the patient's blood flow, blood pumps may augment or replace the pumping action of the heart. For example, a blood pump may be configured as ventricular assist device or “VAD.” Where a VAD is used to assist the pumping action of the left ventricle, the device draws blood from the left ventricle of the heart and discharges the blood into the aorta.
To provide clinically useful assistance to the heart, blood pumps must impel blood at a substantial blood flow rate. For an adult human patient, a ventricular assist device may be arranged to pump blood at about 1-10 liters per minute at a pressure differential across the pump of about 10-110 mm Hg, depending on the needs of the patient. The needs of the patient may vary with age, height, and other factors.
It is desirable to monitor the rate at which blood is impelled by a blood pump. For example, if a VAD is operated at a flow rate in excess of the inflow rate of blood to the ventricle, the VAD will create a suction condition within the ventricle, wherein the ventricle is collapsed and essentially devoid of blood. This condition is undesirable. In this condition, the flow rate through the pump will decline rapidly. Likewise, if the intake or outlet of the pump is occluded, the flow rate will decline gradually. If the flow rate through the pump declines, either rapidly (e.g., as a result of suction condition) or gradually (e.g., as a result of an obstruction or occlusion) to the extent that the flow rate is insufficient, the device will not provide sufficient circulatory assistance to the patient. Excessive flow also can create undesirable conditions. Therefore, it would be desirable to provide a blood pump controller which can monitor the blood flow rate produced by the blood pump which it controls.
Further, when monitoring the blood flow rate, it is desirable to identify whether a decline in flow rate is the effect of a suction condition or the effect of an occlusion. Although both suction and occlusion conditions result in a decline in blood flow rate, these conditions are generally treated differently in order to overcome each respective condition. Moreover, it is often undesirable to treat an occlusion in the same manner as a suction condition would be treated. It is likewise undesirable to treat a suction condition in the same manner as an occlusion would be treated. Therefore, it is desirable to provide a blood pump controller that is capable of differentiating between a blood flow decline caused by a suction condition and a blood flow decline caused by an occlusion.